finding an element in an array by comparing it with another array

Question

I have a matrix

a = [ 1 \'cancer\'
      2 \'cancer\'
      3 \'cancer\'
      4 \'noncancer\'
      5 \'noncancer\' ]

I have another matrix wi

Answer 1

You can use ismember:

a = { 1 'cancer'
      2 'cancer'
      3 'cancer'
      4 'noncancer'
      5 'noncancer' };

  b = [ 4
      5
      2 ];

 a(ismember([a{:,1}], b),:)

This results in

ans = 

    [2]    'cancer'   
    [4]    'noncancer'
    [5]    'noncancer'

To display the results in the order specified by b use (as requested in a follow-up question: In the same order, finding an element in an array by comparing it with another array)

[logicIDX, numIDX]  = ismember(b, [a{:,1}]);
a(numIDX, :)

This results in:

ans = 

   [4]    'noncancer'
   [5]    'noncancer'
   [2]    'cancer'